Search for: [Description = "The second is currently defined by the microwave transition in cesium atoms. Optical clocks offer the prospects of stabilities and reproducibilities that exceed those of cesium. This paper reviews the progress in frequency standards based on optical transitions, recommended by International Committee for Weights and Measures, as a secondary representation of the second. The operation of these standards is briefly described and factors affecting stability and accuracy of these and some new optical clocks are discussed."]
